The structure and physiology of the heart by National Cancer Institute, adapted by Newsela staff, 10/26/17

The heart displayed inside the chest cavity. Photo from Wikimedia Commons

Cells need oxygen to live. Oxygen is in the air we breathe, and our blood carries it to the rest of the body. But this would not happen without the heart.

Your heart is the organ that fuels your whole body. It is about as big as a closed fist. Thanks to your heart, blood continues to flow and keeps your cells healthy and alive.

ChambersOfTheHeart

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Structure of the heart. Image from Wikimedia.

The heart is divided into four spaces. These spaces are known as the right atrium, right ventricle, left atrium and left ventricle.

The two atria take in blood from the veins, while the two ventricles pump blood out of the heart. The walls of the ventricles are thicker than those of the atria. This is because the ventricles need to use more force when they pump.

The right atrium takes in blood that does not have much oxygen. The left atrium takes in blood that does have oxygen, which it picked up from your lungs.

ValvesOfTheHeart

Any good pump needs valves to work. Otherwise, fluid could flow in the wrong direction when it gets squeezed. Since the heart is a pump, it uses valves to make sure the blood keeps flowing forward. Valves are like doors that can open or close shut.

When the ventricles squeeze, certain valves close to stop blood from flowing back into the atria. When the ventricles relax, a different group of valves closes shut. These valves stop blood from flowing back into the ventricles.

PathwayOfBloodThroughTheHeart

The heart does not just work as one pump, but as two. Both pumps are always working at the same time.

Blood flows from the right atrium to the right ventricle, and then gets pumped to the lungs to pick up oxygen. From the lungs, the blood flows to the left atrium, then down to the left ventricle. From the ventricle, it gets pumped to the rest of the body.

TheMyocardium

The parts of the heart wall. The myocardium is in the middle. Image: Blausen.com/Wikimedia.

But who tells the heart to squeeze and relax? The walls of your heart have a muscle inside them. This muscle is called myocardium.

The myocardium is what makes the heart squeeze and relax. Like other parts of the body, it needs oxygen to work.

PhysiologyOfTheHeart

Note that you never need to tell the heart when to beat. In fact, doing this is impossible. Your heart muscles are controlled by a group of cells called the conduction system.

Your conduction system sends 70 to 80 impulses each minute. These are messages that set the rhythm of your heartbeat. In other words, the conduction system controls how fast your heart tightens and relaxes.

CardiacCycle

A single heartbeat is also called a cardiac cycle. During one cycle, the heart tightens and relaxes once. The part of the heartbeat when the heart tightens is called systole. The part when it relaxes is called diastole. At a normal heart rate, one cardiac cycle is less than a second long. This means that, during a person's life, the heart can beat billions of times without stopping.

HeartSounds

Doctors often use your heartbeat to tell if you're healthy. They put a stethoscope on your chest and listen. What they're listening to is the sound of the valves in your heart closing. Heart sounds that are not normal are called murmurs.

HeartRate

Listening to the heartbeat also tells you how fast the heart is beating. This is called the heart rate. Most changes in the heart rate come from the brain, based on how much blood needs to flow through your body. If you jump up and down quickly, your heart needs to work faster to keep the body going.

But your heart rate can also change based on your emotions and body temperature. For example, your heart might beat faster if you see someone you like or you get scared. This might be why ancient Egyptians thought that people's emotions were kept in the heart. Little did they know that emotion and temperature are picked up by the brain.

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Possible response options: ● Describe two things you learned about how the heart functions. ● Describe two things you learned about how the heart is structured. ● Pick a passage from the article and respond to it.